Liquid phase chromatography and extraction techniques are dependent on the interaction of a region bonded to a solid support, such as silica, and a solvent environment containing solutes of interest. The support is stationary with respect to the liquid or solvent phase. The interacting region is designated as the bonded phase or interphase. A general overview of this technology may be found in C. Horvath, Silylated Surfaces (1980), p. 269. Features which contribute to a successful bonded phase include reproducible, non-bonding interactions with solutes in the mobile phase under a variety of operating conditions, such as temperature, pressure, the nature of the solvent and the stability of the interaction over a period of time.
The most widely used of such bonded phases is a hydrophobic phase which may be derived from octadecyl functional silanes. For example, octadecyldimethylchlorosilane- and octadecyltrichlorosilane-treated silica are the most widely used bonded phases for high pressure liquid chromatography (HPLC) and solid phase extraction, respectively. These compounds terminally bond to the silica using a Si--O--Si bond.
In general longer, extended chain length is desirable to provide more interaction of the chain with the material of interest such as the solute. However, octadecyl (C18) has been considered a natural limit for two principle reasons. First, as linear chain length increases, chain folding is induced, particularly when the mobile phase is polar, such as water/acetonitrile combinations. The chain folding process reduces the ability of the bonded phase to interact with the material of interest. In the extreme case, crystallization of the bonded phase occurs resulting in minimal interaction. Second, difficulty is encountered in obtaining pure, higher olefins at practical economics. The oligomerization process for higher .alpha.-olefins produces mixtures which are increasingly difficult to purify at higher molecular weights, with .alpha.-olefins of a length greater than twenty carbon atoms available at purity levels of only about 50%. As such, for practical purposes, the highest number olefin used for chromatographic and extraction purposes is an 18 carbon atom chain length. Information concerning the hydrosilylation of olefins may be found in the textbook entitled, B. Marciniec, ed., Comprehensive Handbook on Hydrosilylation (1992).
As such, there is a need in the art for a material for forming an improved bonded phase which has increased bonded phase interaction while minimizing the effect of chain folding and protecting the Si--O--Si bond between the silanes and the support from hydrolytic attack. Further, there is a need for a simple synthesis reaction for forming an alkylsilane having a relatively long chain length with a high level of purity for use in a bonded phase.